In considering the question of how giraffes got so tall, it’s important to take into account the various aspects of their life history, birth being one of the high points. Here’s some video from the PBS documentary “Tall Blondes” (there’s a halfway decent companion book of the same name) featuring the birth of a baby giraffe;
There’s also video from the San Francisco Zoo showing a first-time mother giving birth, which is interesting in contrast with the “smooth” birth in the first video;
It’s somewhat interesting to consider that the giraffe has been adapted into a long-legged, long-necked form but there doesn’t seem to be any behavioral adaptation to reduce the fall of the offspring when its being born. While such births are often recorded for documentaries, I have to wonder what the mortality rate is for giraffe births, i.e. if any are done harm by the initial fall. How do such rates differ from the mortality rates of other African browsers like gerenuks? While we’re at it, what are the mortality rates among giraffes at different times of life, and what causes those deaths?
I also think that some relatively simple comparative anatomy might help answer some questions about form & function in giraffe evolution. Why not take measurements of upper leg (humerus/femur to radius & ulna/tibia & fibula) of various browsers in the same ecology as giraffes over their evolutionary history and determine what advantages the differing lengths might have as far as running/walking speed or efficiency. Giraffes certainly couldn’t have achieved their long necks without changes to their leg length as well, and the more we can understand and compare about each of the components the better we’ll be able to understand the evolution of the organism rather than just an aspect of an organism.
While I’m speculating, I also have been thinking about the sexual selection model of giraffe evolution that has been proposed and debated. Personally, I don’t find the male combat aspect of it particularly convincing, but this doesn’t mean sexual selection would not be valid; giraffes are derived from shorter-necked ancestors and so the “necking” behavior exhibited by extant males may have developed once a longer neck had been established. What if giraffe ancestor females preferred males with longer necks or if such males had a higher chance of intimidating other males (being a “winner”)? Then, a longer neck would be favored through sex and through an advantage of browsing a larger area, being doubly effective. It is important to note, however, that the necks could not extend on their own; legs and other systems would have develop along with the lengthening of the neck. The development of the giraffe’s specialized circulatory system (when it happened, precisely how it happened [were there relatively long-necked giraffes without it that didn’t fare well?]) is also a big question, but if the mystery of the giraffe can be deciphered perhaps it will not only benefit us in the breadth of our knowledge, but also through using a more integrated approach to evolutionary study. Hopefully one day I’ll be able to study them in their own habitat (else what I do is primarily hypothesis without observation), and perhaps then I’ll be able to answer some of my own questions.